The invention relates to transcoding, and more particularly, to an audio and video synchronizing method in a transcoding system.
In general, transcoding is a core technology for supporting and solving a ubiquitous computing environment across any network, any device, and any content by outputting a single piece of content through various networks and terminals.
Recently, an MP4 file format (MPEG-4 Part 14) is being widely used owing to portable media reproducers, for example, cellular phones, smart phones, MP3 players, etc. The MP4 file format (MPEG-4 Part 14) was created on the basis of Apple's QuickTime container format, and is widely used in formats of MP4, 3GPP, etc. according to applications.
General media files or streams consist of video of more than one track and audio of more than one track. Each piece of video and audio includes time information for exact synchronization when reproduced. When media that is synchronized with audio and video is generally converted into a different format of a container, audio and video are often unsynchronized due to two factors. First, long-term jitter may occur during conversion of time information. Second, packet loss may occur during a stream input.
When media in which loss does not occur is converted into a different container, audio and video must be synchronized theoretically. However, each container uses a time information storage method. A difference in an expression of time causes low amount of jitter. When pre-processing such as a frame rate conversion or a sampling rate conversion is performed, additional jitter may occur. If a long time file is converted without compensating for the jitter, the more the reproduction time increases, the more the audio and video are unsynchronized.